Beautiful thoughts to you all.
I'm not sure what sort of counselling or support you and your wife have received, but I can recommend Doris Zagdanski's books. Doris and her husband, whom I worked with for a few years, lost one of their daughters to SIDS. I know that one of her books deals specifically with explaining death to children. This may well help with your little one's siblings. Just a thought.
Modified by entity at 2:48 PM 10-17-2007